Patients suffering from asthma or any of many other lung diseases require delivery of medication to the bronchi or to the lungs. At the present time, there are two major ways of delivering aerosol treatment or medication to such patients, namely nebulizers, which may be of the venturi-jet type, or of the ultrasonic type which produce aerosols from drug solutions, and metered dose inhalers consisting of pressurized canisters containing Freon and the drug, or alternatively, powder inhalers.
Metered dose inhalers in general are superior to nebulizers, because they are readily portable, they do not require an external power source such as compressed air or electricity, and they are capable of generating aerosols that are suitable for inhalation.
The problem with Freon driven units is that hydrofluorocarbons are being limited in quantity, or phased out, because of their effect on the upper ozone layer.
Existing powder inhalers may use unit doses consisting of small cartridges or capsules which are in some way broken open so that the powder can be inhaled. Alternatively, there are some devides that may contain multiple doses in a small hopper, and a metering system to assure that each dose is similar. These latter devices are generally superior in that they are activated by the patient's inhalation, rather than by Freon.
Up to the present time, the inhalers that have been the most popular have been those that consist of a Freon pressurized canister containing the drug particles. These devices generate a droplet aerosol consisting of Freon and the drug particles. The Freon evaporates rapidly, and leaves small drug particles of about three microns aerodynamic mass median diameter available for inhalation. Thus, aerosol particles are made available to patients, not only for maintenance treatment, but also for extremely ill patients who have very little inspiratory flow rates. However, with the current unpopularity of hydrofluorocarbons, continuing efforts have been made to utilize crystalline powders of the drug material without the need to use a pressurization system containing Freon.
There are some currently available powder inhalation systems, but they do not function effectively unless the patient can generate flow rates over approximately 20-30 liters per minute, since it is the patient's inhalation that mobilizes the powder and prepares it for inhalation, in contrast to the metered dose inhaler which uses Freon to mobilize the powder. The problem of such current powder inhaler systems is that they require strong inhalation on the part of the patient. Accordingly, they may be useful for maintenance treatment of patients with chronic bronchitis, emphysema and asthma, but they not work effectively or at all in people with severe asthma attacks, or those who have deterioration of their chronic bronchitis or emphysema related to respiratory infections.